1. Technical Field
The present invention relates to a donor substrate for laser transfer and an organic electroluminescence display device manufactured using the same. More particularly, the invention relates to a donor substrate used to form an organic layer for an organic electroluminescence display device, and an organic electroluminescence display device using the same.
2. Related Art
In general, an organic electroluminescence (EL) display device is composed of several layers, such as, for example, an anode, a cathode, a hole injecting layer, a hole transporting layer, an emission layer, an electron transporting layer, and an electron injecting layer. Organic electroluminescence display devices may be classified into polymer organic electroluminescence display devices and small molecule organic electroluminescence display devices according to the material used therein. In the case of the small molecule organic electroluminescence display device, each of the layers is formed by a vacuum deposition process; in the case of the polymer organic EL display device, the electroluminescent (EL) element may be manufactured by a spin coating process.
For monochrome devices, an organic electroluminescence display device using a polymer may be simply manufactured by a spin coating process, and needs a lower driving voltage compared to the device using small molecules, but it has disadvantages in efficiency and life span. Further, the manufacture of full color devices requires polymers of red, green and blue colors to be patterned, which leads to degradation of such luminescence characteristics as efficiency and life span when an inkjet technique or a laser-induced thermal imaging method is used for patterning.
In particular, when the laser-induced thermal imaging method is used for patterning, most single polymers are materials which are not transferred. A method of forming a pattern of a polymer organic electroluminescence display device using a laser-induced thermal imaging method is disclosed in Korean Patent No. 1998-51844, and also in U.S. Pat. Nos. 5,998,085, 6,214,520 and 6,114,088.
The application of the laser-induced thermal imaging method needs at least a light source, a transfer substrate, and a substrate, wherein light emitted from the light source is absorbed into a light absorption layer of the transfer layer and is converted to thermal energy. The thermal energy allows the material forming the transfer layer to be transferred onto the substrate so that a desired image is formed (see U.S. Pat. Nos. 5,220,348, 5,256,506, 5,278,023 and 5,308,737).
This laser-induced thermal imaging method has been used to manufacture a color filter for a liquid display device, and has also been used to form a pattern of an electroluminescent material (see U.S. Pat. No. 5,998,085).
The invention of U.S. Pat. No. 5,937,272 is directed to a method of forming an advanced patterned organic layer in a full-color organic electroluminescence display device. The method uses a donor support technique in which an organic electroluminescent material is coated with a transferable coating material. The donor support is heated so as to cause the organic electroluminescent material to be transferred onto a recessed surface of a substrate that forms a colored organic electroluminescent medium in an intended underlying pixel. At this time, heat or light is applied to the donor substrate so that the electroluminescent material is vaporized and transferred to the pixel.
In U.S. Pat. No. 5,688,551, a sub-pixel is formed in each pixel region by transfer from a donor sheet to a receiver sheet. In the transfer process, a sublimated organic electroluminescent material is transferred from the donor sheet to the receiver sheet at a low temperature (e.g., about 400° C. or less) so as to form the sub-pixel.
The polymer constituting the emission layer has a large molecular weight and thus the adhesion strength of the substrate becomes larger after laser transfer. Accordingly, the patterning by laser leads to poor transfer characteristics.
As a result, a shadow mask technique has been recently used for R, G and B patterning of the full-color organic electroluminescence display device. Thus, it would not be suitable for the patterning of a large-sized display device.
Recently, a polymer with a structure suitable for a photolithographic process was developed in order to manufacture a full-color organic electroluminescence display device by patterning red, greed and blue emission layers. However, in the latter method, because a photoacid generator is mixed to cure an exposed portion, impurities may be introduced, other active materials may be damaged by super acid generated upon curing, and the inflow of impurities may occur, all of which unreasonably affects the stability or life span of the device.